CD4 vs. Viral Load: What’s in a Number?

CD4 vs. Viral Load: What’s in a Number?

Viral load and CD4 count

If you’ve been diagnosed with an HIV infection, your doctor will keep a sharp eye on your viral load and CD4 count. These metrics speak volumes about your HIV status and health. They provide important information on:

  • the health of your immune system
  • the progression of your disease
  • whether it’s time to begin HIV therapy
  • how your body is responding to treatment

What is a CD4 count?

A CD4 count is a blood test that your doctor can use to check the level of CD4 cells in your body. CD4 cells are a type of white blood cell that play an important role in your immune system. They’re also called T-cells. They alert other immune cells to the presence of viruses and bacteria in your body.

Certain receptors on your CD4 cells make them prime targets for HIV. If you contract an HIV infection, the virus will attack your CD4 cells. This will cause the number of CD4 cells in your body to drop, weakening your immune system.

A normal CD4 count ranges from 500–1,600 cells per cubic millimeter, reports If your CD4 count is lower than 200 cells per cubic millimeter, your doctor may diagnose you with the clinical stage called AIDS, or acquired immunodeficiency syndrome (AIDS). At this stage, the body’s immune system is weak due to the low number of CD4 cells available to fight disease. This leaves the body susceptible to infections.

What is a viral load?

Your doctor can order a viral load test to assess the level of HIV in your body. It measures the number of HIV virus particles in a milliliter of your blood. Those particles are also known as “copies.”

A low viral load is a sign of the virus copying itself in low amounts in the body. According to, HIV viral load is typically undetectable below levels of 40–75 copies/mL. The goal of HIV therapy is to lower your viral load below the detectable level.

Why is it important to consider multiple test results?

A single test result can only tell you so much about your CD4 levels, viral load, and overall health. The numbers often vary from one test to another.

For example, after contracting HIV, there is a period when the virus makes several copies, leading to a viral load spike. Once your immune system responds to it, it will decrease to a base level. The time of day, any illnesses you have, and recent vaccinations can also affect your CD4 count and viral load.

As a result, it’s important to consider trends in your test results, rather than just individual test results.

When will your HIV treatment begin?

Your CD4 count and viral load will guide your doctor’s treatment plan. The question of when to start your HIV treatment is best decided on an individual basis considering a variety of factors. Your doctor will likely encourage you to start HIV therapy if your CD4 counts fall below 350 cells per cubic millimeter. They may begin your therapy earlier if your CD4 counts are as high as 500 cells per cubic millimeter but you’re experiencing a rapid drop in your CD4 count or you have a high viral load.

According to the World Health Organization (WHO), recent studies suggest there are benefits of beginning HIV therapy early, when your CD4 counts are higher than 350 cells per cubic millimeter. It appears to reduce your risk of developing:

  • AIDS
  • tuberculosis
  • non-AIDS-defining illnesses, such as liver failure and heart disease

Early treatment may also lower your chances of spreading HIV to other people by preventing a larger viral load.

HIV therapy is also called antiretroviral therapy (ART) or highly active antiretroviral therapy (HAART). It consists of a combination of antiretroviral drugs (ARV) designed to keep the virus from spreading by targeting different proteins or mechanisms the virus uses to replicate. Slowing the spread of HIV gives your immune system and CD4 count time to recover. A combination of at least three drugs is used to reduce the likelihood of the virus developing resistance to your treatment.

Your doctor may also recommend changes to your diet or other lifestyle habits to help increase your CD4 count and promote a healthy immune system.

How will your doctor monitor your condition?

To monitor your condition, your doctor will likely conduct CD4 counts and viral load tests every three to six months. The schedules for each test may differ slightly. When you first begin treatment for HIV, and when you change any medications to your regimen, your doctor may conduct these tests more frequently. Once your treatment seems to be working well, they may conduct these tests less often.

HIV treatment has come a long way in recent years. Following your doctor’s recommended treatment plan and leading a healthy lifestyle can help you keep your CD4 count high and your viral load low. Early treatment and effective monitoring can help you manage your condition, reduce your risk of complications, and live a longer and healthier life.

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